1. Field of the Invention
The present invention relates to a telecommunication network based on distributed control which enables the construction of an economical and highly flexible telecommunication network even if there is a large number of switch subsystem nodes, by separating the control subsystems and switch subsystems of a switch node system and freely distributing their arrangement inside the network.
This application is based on patent application No.Hei8-249985 filed in Japan, the content of which is incorporated herein by reference.
2. Background Art
In conventional switch node systems, the switch subsystem and the control subsystem for controlling the switch subsystem are provided on a single node. While there are system organization wherein the control subsystem and the switch subsystem are provided on separate nodes (the node in which the control subsystem is provided is referred to as the "central office" and the node in which the switch subsystem is provided is referred to as the "remote office"), these have the control subsystem and the switch subsystem permanently connected by a dedicated line, thus making it impossible to make connections other than those which are set. Hence, such system organization are not sufficiently flexible to be applied to situations in which dynamic connections of the remote offices is required, situations of dynamic switching to other central offices in failure of the central office, and situations wherein the central office is merged into the remote office side to solely control the enlarged switch subsystem by a control subsystem.
FIG. 2 is a diagram showing an example of the structure of a conventional switch node system, and FIG. 3 is a diagram showing an example of a conventional remote controlled switching system.
A conventional switch node 1 comprises a switch fabric device 4 for switching multimedia information such as audio or data between a subscriber lines 2 and a trunk lines 3, and a controller 5 for sending various control orders to the switch fabric device 4 to perform connection operations. While the controller 5 uses a high-performance processor in order to simultaneously control multiple subscriber lines 2 and trunk lines 3, since such high-performance processors have extremely high processing capacity, the processing capacity often exceeds that required by the switch fabric device 4, thus resulting in surplus processing capacity.
Therefore, remote controlled switching system organizations have been proposed as shown in FIG. 3 wherein a plurality of switch fabric devices 6-1, 6-2, . . . 6-n are each positioned near subscribers and these are remotely controlled by a single controller 7. Examples of such remote controlled switching systems are described in "A Survey of Bell System Progress in Electronic Switching"; The Bell System Technical Journal, pp. 937-997, July-August 1965 and Habara, Goto and Suzuki, "DEX-R1 and DEX-R3 Electronic Switching Systems", Kenkyuu Jitsuyouka Houkoku, Vol. 23, No. 5, pp. 955-968 (1974).
FIG. 4 is a diagram showing an example of a conventional remotely controlled switching system, described in the Habara's reference.
In FIG. 4, reference numeral 10 denotes a central office having various control-related devices, reference numeral 11 denotes a central controller generally referred to as a "processor" for executing connection control programs to control remote offices 20-1, 20-1, . . . , 20-n, reference numeral 12 denotes a main memory for storing connection control programs and their control data, reference numeral 13 denotes a channel multiplexer activated by the central controller 11 for controlling data transfer between the main memory 12 and a remote controller 15, reference numerals 14-1 and 14-2 denote general subchannels for transferring data between the main memory 12 and the remote controller 15, reference numeral 15 denotes a remote controller for executing data transfer between the central office 10 and the plurality of remote offices 20-1, 20-2, . . . , 20-n, reference numerals 16-1, 16-2, . . . , 16-n denote control information links which make one-to-one connections over dedicated lines between the central office 10 and the plurality of remote offices 20-1, 20-2, . . . , 20-n, and 20-1, 20-2, . . . , 20-n are remote offices which are remotely located with respect to the central office 10 and contain the various devices of the switch subsystem. Additionally, inside the remote office 20-1, reference numeral 21 denotes a remote office data sender-receiver for transmitting and receiving data with the central office 10, reference numeral 22 denotes a switch fabric device, reference numeral 23 denotes a switch fabric for conveying information such as audio data, and reference numeral 24 denotes a switch controller for receiving data from the remote office data sender-receiver 21 and sending control orders to the switch fabric 23 or receiving data from the switch fabric 23.
Hereinbelow, when referring to devices such as the remote offices 20-1, 20-2, . . . , 20-n which have identical structures, the suffixes (such as -1 and -2) shall be omitted from the reference numerals when they are unnecessary for the purposes of describing the invention.
FIG. 5 is a diagram showing a conventional switch control method.
A method for controlling a plurality of remote offices 20 with a single central office 10 using the structure shown in FIG. 4 shall be explained. FIG. 5 shows a send mode wherein control data are sent from the central office 10 to the remote offices 20, and a receive mode wherein control data are read from the remote offices 20 by the central office 10.
First, under direct control, in other words when the controller 5 and the switch fabric device 4 are integrated on a single switch node such as shown in FIG. 2, in the send mode, a drive order is sent from the controller 5 to the switch fabric device 4 by the controller 5 executing a switch fabric control dedicated instruction (DTO instruction) 30 which includes a drive order for controlling the switch fabric device 4 or a switch fabric control dedicated instruction (DTO instruction) 31 which indirectly designates a drive order 32. The switch fabric device 4 receives, interprets and executes the control order, and upon completion of the procedure, the controller 5 receives a completion signal from the switch fabric device 4 to complete the execution of the instruction. In this way, the dedicated instructions 30 and 31 are executed basically in the same way as a memory write access instruction.
On the other hand, under remote control, in other words when the controller and the switch fabric devices are remotely located as shown in FIG. 3, in the send mode, a drive order 43 is basically sent by an input/output channel command. That is, the central controller 11 of the central office 10 executes an input-output instruction (SIO instruction) 40 and activates the channel multiplexer 13. The channel multiplexer 13 sequentially reads a command address word (CAW) 41 and a channel command (CCW) 42 from the main memory 12, and activates the general subchannel 14-1. The general subchannel 14-1 reads the switch fabric drive order 43 from the area in the main memory 12 designated by the CCW 42 and sends the switch fabric drive order 43 to the remote controller 15. The remote controller 15 sends the drive order 43 to the remote office data sender-receiver 21 via the control information link 16-1. The remote office data sender-receiver 21 transfers the drive order 43 to the switch controller 24, the switch controller 24 checks and interprets the drive order 43, and the switch fabric 23 is made to perform the desired switching operation. Once the switching operation is completed, the remote office data sender-receiver 21 returns an execution completion signal to the remote controller 15 via the control information link 16-1. When the remote controller 15 sends an execution completion signal to the general subchannel 14-1, the channel multiplexer 13 causes an interrupt to the central controller 11. The central controller 11 analyzes the cause of the interrupt to find that the execution of the switch fabric drive order has been completed. The designation of which of the plurality of remote offices 20 are to be controlled is done by the channel number field of the channel instruction 40. Thus, a single central office 10 is capable of transferring control information between a plurality of remote offices 20 by using sets of CAW 41, CCW 42 and switch fabric drive order 43 which are different for each channel number.
Next, in the case of the receiving mode (data transfer from the switch subsystem to the control subsystem) under direct control (control subsystem and switch subsystem housed in the same node), a dedicated instruction (DTN instruction) 52 indirectly designating a scan order 53 or a dedicated instruction (DTN instruction) 50 including a scan order for the switch subsystem are executed by the controller 5 of FIG. 2. Due to the execution of the DTN instruction, the internal status of the switch fabric device 4 is read and written into the scan result area 51 or 54.
On the other hand, in the receive mode under remote control, the switch fabric scan results are read by a method similar to the case of the send mode under remote control, that is, by execution of an input-output channel command. Specifically, the central controller 11 in FIG. 4 executes the input-output instruction (SIO instruction) of FIG. 5 and activates the channel multiplexer 13. The channel multiplexer 13 sequentially reads the command address word CAW 61 and the channel command CCW 62 in the main memory 12, then reads a scan order 63 from the main memory 12 by the first command CTL of the channel command CCW 62, then sends the scan order 63 to the remote controller 15 via the general subchannel 14-1. The remote office data sender-receiver 21 transfers the scan order 63 to the switch controller 24, and the switch controller interprets and executes the scan order 63 to read the internal status of the switch fabric 23 and return the scan results to the remote office data sender-receiver 21. Due to the remote office data sender-receiver 21 returning the scan results to the remote controller 15 via the control information link 16-1, the general subchannel 14-1 completes the execution of the command CFL and initiates the execution of the next command RCM in the channel command CCW 62. In accordance with the command RCM, the scan results received from the remote controller 15 are written into the designated scan result area 64 in the main memory 12. As the command RCM requires "n"-times read accesses by sending the read requests to and receiving the replay data from the remote office 16-1 over the control information link 16-1, the space propagation delay will increase with the distance between the central office 10 and the remote office 16-1. Once the writing into the scan result area 64 is completed, the channel multiplexer causes an interrupt in the central controller 11. The central controller 11 analyzes the cause of the interrupt to find that the execution of the switch fabric scan order has been completed.
FIG. 6 is a diagram showing a conventional identification method for multiple switch fabrics.
In FIG. 6 the same program is used in a central office to identify and select control data (referred to as primary data) corresponding to each of the plurality of remote offices 20.
First, an area in the main memory 12 is divided into areas 71 and 72 of fixed sizes corresponding to the remote offices, and the data structures are made to be identical between the remote offices. For example, in FIG. 6, reference numeral 71 denotes a data area (#1 office primary data area) corresponding to remote office 20-1, reference numeral 72 denotes a data area (#2 office primary data area) corresponding to remote office 20-2, and the data areas 71 and 72 are given the same data structure. Next, the connection control program in the central office 10 is shared between the remote offices 20-1 and 20-2. The connection control program includes a primary office data access instruction 70 whose base address register field 74 specifies the top address of the primary office data area. For example, when controlling the remote office 20-1, the top address (b1 in FIG. 6) of the #1 office primary data area 71 is preloaded. Additionally, controlling the remote office 20-2, the top address (b2 in FIG. 6) of the #2 office primary data area 72 is preloaded. By switching the value of the base register over time by dividing into time intervals for controlling each remote office such as by entering the value of b1 into the base register in one time interval and entering the value of b2 at a different time interval, it is possible to control a plurality of remote offices 20 on a time-shared basis.
The above mentioned remote control switching system is considered as one type of the distributed switching system and the other type of distributed switching system is a LAN(Local Area Network)-based distributed switching system in which the controller and the switch fabric devices are connected not by dedicated lines as in a remote control switching system, but instead are connected by a LAN (Local Area Network) has been proposed. In this distributed switching system, call connection control is performed under the cooperation of the controller (central processing-management module) and the switch fabric devices (switching modules) by sending and receiving through a LAN (Japanese Patent Application, First Publication No. Sho 62-188590).
All these direct control and remote control switching systems and LAN-connected distributed switching systems have the following problems.
(1) In the structure shown in FIG. 4, the central office 10 and the remote offices 20 are connected one-to-one by the dedicated lines 16, thus requiring general subchannels 14, dedicated lines 16 and remote office transmitter-receivers 21 to be provided in numbers proportional to the number of remote offices being controlled, and also requiring the channel multiplexer 13 and the remote controller 15 to be expanded to accommodate the number of remote offices. For this reason, if the number of remote offices becomes too numerous, the overall network requires an extremely large number of devices, hence greatly increasing the cost.
(2) Additionally, since the control subsystem and the switch subsystem are permanently connected by means of dedicated lines, it is not possible to make any connections other than those which are set up. For example, the system is not flexible enough to perform dynamic connections of the remote offices with low usage to share control information links and reduce the network cost, or to dynamically switch to other central offices when the central office is down.
(3) Additionally, the communication means or methods for the case of direct control in which the controller and the switch fabric devices are in the same node and the case of remote control in which the controller and the switch fabric devices are located remotely are different, so that the application program must include separate codes for direct control and remote control. This courses high development cost and low flexibility.
(4) Furthermore, since the control data is transferred through channel commands in the case of remote control, the software overhead for the preparation, activation and interrupt processing for channel commands is large and inefficient.
(5) Also, since the transmission of data between the remote controller 15 of the central office and the remote office data sender-receivers 21 of the remote offices is performed by the remote read access command, such as the RCM command in the case of remote control, the time delay due to spatial propagation increases as the distance between the central office and the remote offices increases, thus extending the waiting time until the remote controller 15 receives confirmation signals from the remote office data sender-receivers 21 so as not to allow shifting to the next data transmission. In this way, the decrease in performance is considerable in the case of remote control over long distances.
(6) Furthermore, as a conventional method for identifying and controlling a plurality of switch fabric devices, the designation of channel numbers 40 and 60 as shown in FIG. 5 and the switching of control data by switching the value of the base register (b) as shown in FIG. 6 are combined. However, when designating channel numbers, the number of remote offices capable of being controlled is limited by the length of the channel number field, and in the base register switching method the data configurations of the switch fabric devices must be made completely identical, thus making this system unsuitable for general applications and poor in flexibility.
(7) Additionally, in switching systems connected by LANs, the switching system is distributed over a range covered by a LAN by dividing the system into a plurality of modules such as a switching module and a central processing module. Even if these distributed systems are introduced in the network, the network structure is still the same as the one, constructed form conventional switch system. Each switching systems are self-contained and independent of each other, thus giving the network overall an inflexible structure which is unsuitable for general applications and poor in flexibility.
(8) Furthermore, in switching systems connected by LANs, the network is constructed under the assumption of confinement to a local area, so that there are a variety of restrictions such as restrictions to the number of modules able to communicate and the distance between modules.